ENERGY customers are facing “infuriating” waits to get through to call centres, while some online queries are going unanswered, a watchdog has found.

Spark Energy, which went bust last week, was the worst firm for call waiting times, leaving customers on hold for 27 minutes and 21 seconds on average over the course of the investigation by Which?, potentially costing a mobile user £15.

The consumer group made more than 450 phone calls to 38 gas and electricity suppliers and also tested live chat and email services, finding “huge” variations in how long customers were kept waiting.

Utilita left its customers waiting for an average of 24 minutes and 19 seconds and had the longest single call waiting time of 72 minutes and 40 seconds.

Five of the Big Six energy firms kept customers waiting for around 10 minutes or longer on average – with Npower the worst on 20 minutes and 31 seconds.

Scottish Power was the best of the Big Six with an average call waiting time of three minutes and 29 seconds, while smaller supplier Affect Energy took just 10 seconds to answer followed by So Energy on 21 seconds.

Npower was by far the worst supplier for live chat response times, taking more than 17 minutes on average before a customer service adviser responded.

It was followed by SSE and Eon, which both took more than four minutes on average.

Which? said Eon customers might consider themselves lucky to get a response at all after finding that live chat was unavailable on 10 out of 12 attempts.

Utilita answered live chat enquiries in 93 seconds on average but was unavailable on seven out of 12 occasions.

Engie and Economy Energy did not offer live chat but failed to answer any of the watchdog’s 12 emailed or online form enquiries within two weeks.

Alex Neill, Which? managing director of home products and services, said: “As if regular price hikes aren’t bad enough, customers of some energy companies are facing infuriating waits just to get through to a customer service adviser on the phone. No one should have to put up with shoddy customer service and rip-off deals.”